1. Field of the Invention
The present invention relates to a power generation control apparatus that controls an amount of power generation by a power generator incorporated in a vehicle.
2. Background Art
As is described in Patent Document 1, there is a method of controlling an amount of power generation by a power generator according to a battery condition, such as a battery voltage, a battery current, and a battery operating temperature, using a power generation control apparatus equipped with a detection portion detecting the battery condition and a regulator capable of controlling magnitude of a DC voltage generated by a vehicle power generator. According to this method in the related art, a battery state of charge (hereinafter, abbreviated to SOC) calculated on the basis of a current charged to and discharged from the battery is maintained at a target of constant SOC to reduce unnecessary power generation. Accordingly, fuel efficiency is improved while battery exhaustion is prevented.
Patent Document 2 uses a power generation control apparatus that controls the battery SOC to stay at the target SOC as in Patent Document 1. Herein, a maximum value of engine efficiency is computed for every engine speed. By changing the target SOC according to the maximum value of engine efficiency, an amount of power generation is increased in a segment where engine efficiency is high. Consequently, an amount of fuel used for power generation can be reduced.
Further, Patent Document 3 discloses an apparatus that measures an increased amount of fuel for generation of unit generation output (hereinafter, referred to as the generation cost) for every engine operating condition and saves in advance an engine operating range in which the generation cost becomes low. The generation cost becomes lower at an operating point at which the engine is operating under medium load at steady running and becomes higher at an operating point at which the engine is operating under low load at idle or low-speed running. At the time of power generation, an amount of fuel consumed for power generation is reduced by generating power when the engine driving condition falls within the saved operating range. Further, in order to maintain the battery SOC constant at a predetermined value, the power generation range is widened and an amount of power generation is increased in a case where the battery SOC is smaller than the predetermined value whereas the power generation range is narrowed and an amount of power generation is reduced in a case where the battery SOC is larger than the predetermined value. Owing to this configuration, it becomes possible to reduce the generation cost while preventing overcharge and overdischarge of the battery.
Patent Document 1: JP-A-2003-52131
Patent Document 2: Japanese Patent No. 4497150
Patent Document 3: Japanese Patent No. 4158615
The control apparatus of Patent Document 1 controls the battery SOC to be always maintained constant independently of the operating condition of the engine. Accordingly, for example, in a case where the vehicle runs in the city by repeating running under medium load at low generation cost (for example, steady running) and running under low load at high generation cost (for example, idle), it is necessary to generate the same amount of power both at an operating point of high generation cost and an operating point of low generation cost. Hence, this control apparatus has a problem that a large amount of fuel is consumed for power generation.
As is described in Patent Document 3, it is known that an operating point of high engine efficiency and an operating point of low generation cost do not fall on the same operating point. However, because the apparatus of Patent Document 2 sets the target SOC according to the engine efficiency, there is a problem that a large amount of fuel is used for power generation.
The control apparatus of Patent Document 3 determines an engine operating range and an amount of power generation to carry out power generation so as to maintain the battery SOC constant. Accordingly, in a case where the vehicle runs by repeating running under medium load at low generation cost and running under low load at high generation cost, power is generated more frequently during the running under low load at high generation cost. This control apparatus therefore has a problem that a large amount of fuel is consumed for power generation as a result.